1. Field of the Invention
The present invention relates to the design and construction of an engine, in particular an internal combustion engine. More specifically, the present invention relates to the construction and design of various aspects of a continuously variable transmission (xe2x80x9cCVTxe2x80x9d) for an internal combustion engine.
2. Description of the Prior Art
The prior art includes several examples of CVT that have been contemplated for use on a number of vehicles. For example, CVTs have been designed for use on recreational vehicles, such as snowmobiles and all terrain vehicles (xe2x80x9cATVsxe2x80x9d). They have also been designed for automobiles.
A continuously variable transmission is considered to be superior to a traditional geared transmission becase, unlike a traditional gearbox that provides four or five separate gears, a CVT provides a infinite number of different xe2x80x9cgears.xe2x80x9d As a result, CVTs are much more efficient at transmitting torque from the engine to the output shaft of the transmission.
One drawback with CVTs, however, is that they cannot operate in a reverse torque transmission mode (or xe2x80x9cRTTxe2x80x9d). This is due to the belted construction that is a fundamental aspect of CVTs.
When a transmission is operating in an RTT mode, movement of the vehicle containing the transmission is transferred, through the transmission, to the engine to start the engine. This is likened to starting car with a geared transmission by rolling the car down a hill a xe2x80x9cpoppingxe2x80x9d the clutch.
Since CVTs are incorporated in recreational vehicles that can be driven far from a repair station, should the engine starter fail, it is deirable to include a transmission with a RTT mode of operation. This need has become more pronounced recently with the introduction of four stroke engines (as opposed to two stroke engines) in recreational vehicles. Four stroke engines are more difficult to start because the number of components that must be moved in relation to one another to set the system in motion.
In view of the foregoing, it is therefore one object of the present invention to provide a continuously variable transmission that can operate in a RTT mode of operation.
Accordingly, it is one aspect of the present invention to provide a drive pulley for a CVT with a shaft adapted for operative connection to the engine crankshaft. An inner half of the drive pulley is disposed on the shaft, the inner half having a belt engagement surface associated therewith adapted to engage a first side of a belt. An outer half also is disposed on the shaft, the outer half having a belt engagement surface associated therewith adapted to engage a second side of a belt. A slide sleeve is disposed on the shaft adapted to engage an inner side of a belt. In addition, a spring is provided that biases the inner half and the outer half of the drive pulley apart from one another. The slide sleeve freely rotates with respect to the shaft when the belt is engaged thereby and the belt either is stationary or travels in a first direction.
It is still another aspect of the present invention to provide a drive pulley for a CVT that additionally includes at least one groove disposed on an inner surface of the slide sleeve and at least one pin extending from the shaft, the pin being biased to engage the at least one groove.
One further aspect of the present invention is to provide a drive pulley for a CVT where the at least one groove in the slide sleeve comprises three grooves spirally disposed on the inner surface of the slide sleeve and the at least one pins comprises three pins, one each disposed in connection with each groove.
Another aspect of the present invention is to provide a drive pulley for a CVT where the grooves in the slide sleeve each comprise first and second surfaces, the second surface being angled more steeply than the first surface. The first surface permits the pins to slide therefrom when the belt engages the slide surface and the belt either is stationary or travels in the first direction. The second surface permits the pins to engage therewith when the belt travels in a second direction, opposite to the first.
Still another aspect of the present invention is to provide a drive pulley for a CVT where the slide sleeve also includes an annular flange extending outwardly from an outer surface on one end. The annular flange engages at least a portion of the first side of the belt when the belt engages the slide sleeve.
One further aspect of the present invention is to provide a drive pulley for a CVT that also includes at least one antifriction bearing journaling the slide sleeve to the shaft.
An aspect of the present invention is to provide a drive pulley for a CVT where the outer half further comprises at least one centrifugal weight pivotally mounted thereto so that the centrifugal weight swings outwardly upon application of a centrifugal force, applies a pressing force against an associated roller disposed on the outer half, and causes the outer half belt engaging surface to move towards the inner half belt engaging surface, sandwiching the belt therebetween.
An additional aspect of the present invention is to provide a drive pulley for a CVT where the at least on centrifugal weight is provided with a plurality of indentations on its outer surface to engage the roller at specific engine speeds, momentarily delaing the advancement of the outer half belt engagement surface toward the inner half belt engaging surface, and providing an operation comparable to a traditional geared transmission.
One further aspect of the present invention is to provide a driven pulley for a CVT that includes a shaft adapted for operative connection to an output shaft of the continuously variable transmission. An inner half is disposed on the shaft, the inner half having a belt engagement surface associated therewith adapted to engage a first side of a belt. An outer half disposed on the shaft, the outer half having a belt engagement surface associated therewith adapted to engage a second side of a belt. A spring biases the inner half and the outer half together with one another. A connector rotatably couples the inner half with the outer half. The connector is disposed between the inner half and the outer half.
Another aspect of the present invention is to provide a driven pulley for a CVT where the connector comprises a ring having at least one ribbed portion and at least one non-ribbed portion, and the inner half and the outer half both comprise at least one ridged section adapted to engage the at least one ribbed portion of the connector.
Also, it is an aspect of the present invention to provide a driven pulley for a CVT having a toothed wheel fixedly connected to the shaft. A guide member operatively connects to the toothed wheel and has at least one projection adapted to mate with at least one indentation on the inner half.
One aspect of the present invention is to provide a driven pulley for a CVT where the at least one projection on the guide member includes a first ramp with at least one first slope and a second ramp with at least one second slope that is less than the at least one first slope. The first ramp is adapted to engage the inner half during a normal mode of operation of the driven pulley and the second ramp is adapted to engage the inner half during a reverse torque transmission mode of operation of the driven pulley.
A further aspect of the present invention is to provide a CVT including a drive pulley adapted to connect to a crankshaft of an engine. The drive pulley includes a drive pulley inner half disposed on the shaft, the drive pulley inner half having a belt engagement surface associated therewith adapted to engage a first side of a belt. The drive pulley also includes a drive pulley outer half disposed on the shaft, the drive pulley outer half having a belt engagement surface associated therewith adapted to engage a second side of a belt. The drive pulley further includes a slide sleeve disposed on the shaft adapted to engage an inner side of a belt and a spring biasing the drive pulley inner half and the drive pulley outer half apart from one another. The slide sleeve freely rotates with respect to the shaft when the belt is engaged thereby and the belt either is stationary or travels in a first direction. The CVT also includes a driven pulley adapted to connect to an output shaft of the continuously variable transmission. The driven pulley has a driven pulley inner half disposed on the shaft, the driven pulley inner half having a belt engagement surface associated therewith adapted to engage a first side of a belt. It also has a driven pulley outer half disposed on the shaft, the driven pulley outer half having a belt engagement surface associated therewith adapted to engage a second side of a belt. A spring biases the driven pulley inner half and the driven pulley outer half together with one another. A connector rottably couples the driven pulley inner half with the driven pulley outer half, The connector is disposed between the driven pulley inner half and the driven pulley outer half.
One further aspect of the present invention is to provide a pneumatically-actuated driven pulley.
Another aspect of the present invention is to provide a driven pulley for a continuously variable transmission. The driven pulley includes a shaft adapted for operative connection to an output shaft of the continuously variable transmission. An inner half is rotatably disposed on the shaft, the inner half having a belt engagement surface associated therewith adapted to engage a first side of a belt. An outer half rotatably disposed on the shaft, the outer half having a belt engagement surface associated therewith adapted to engage a second side of a belt. A spring biases the inner half and the outer half together with one another. A chamber is disposed relative to the inner half and the outer half, wherein the chamber is adapted to respond to a change in gas pressure therein, which causes the inner and outer halves to clamp onto the belt.
A further aspect of the present invention is to provide a driven pulley where the chamber is disposed between the inner and outer halves, and the change in gas pressure results from the application of a predetermined vacuum to the chamber.
One additional aspect of the present invention is to provide a driven pulley where the vacuum is supplied by an engine.
Another aspect of the present invention is to provide a driven pulley where the vacuum is supplied by a vacuum pump.
An aspect of the present invention also is to provide a driven pulley that includes a pressure connector attached to the shaft, wherein the pressure connector is operatively connected to the chamber.
Still another aspect of the present invention is to provide a driven pulley where the chamber is disposed adjacent to either the inner or the outer half, and the change in gas pressure results from the introduction of a predetermined pressure to the chamber.
Other aspects of the present invention will be made apparent from the description that follows and the drawings appended hereto.